178 Prof. Chapman on some Minerals 



crystals that have come under my observation in these lodes. I 

 have assayed a good many samples for silver without finding any 

 workable quantity of the latter metal. The highest amount that 

 I have obtained corresponds, indeed, to no more than 1^ oz. to 

 the ton of reduced lead. This comparative absence of silver 

 appears to be connected with the very general absence of arse- 

 nical minerals throughout the district. A comparative study of 

 the classical lead-districts of both Europe and this continent will, 

 I think, be found to warrant the conclusion that, where arsenical 

 ores, such as arsenical pyrites, Fahl-ores, &c, are generally 

 absent, the galena will not prove to be argentiferous in a paying 

 point of view. 



3. Marcasite, Fe$ 2 . — The occurrence in Canada of iron py- 

 rites in its trimetric or rhombic condition has not been hitherto 

 announced. I obtained several well-characterized examples from 

 the walls of a large vein, holding galena and copper pyrites, in 

 lot 25 of the fifth concession of the township of Neebing, a few 

 miles east of the Kaministiquia river. In all of these examples 

 tabular prismatic crystals are united somewhat irregularly, but 

 with the basal plane in common, in curved rows, with an acute 

 angle of the prism projecting outwards, and thus forming the 

 variety known as " Cockscomb Pyrites," the " Kammkies" of 

 German authors. In this variety the crystals are not united 

 regularly by a plane of the prism or by one of the macrodome 

 planes, as in the true twins of marcasite, but are simply formed 

 at the free end of the radiating lamella?, the broad surface of the 

 latter representing the basal plane. A point of much interest 

 in connexion with these specimens is the occurrence of common 

 or cubical pyrites in the same vein. The latter species occurs in 

 different parts of this vein in small but distinct crystals — com- 

 binations of the cube and octahedron, with the cube faces pre- 

 dominating. Where representatives of the separate conditions 

 of a dimorphous substance thus occur together, the cause by 

 which the dimorphism was produced is not readily explained. 

 In the present instance there were no data to show that one 

 condition had originated at an earlier or later period than the 

 other ; and yet such must in all probability have been the case. 



Some of the marcasite specimens from this spot had already 

 entered into decomposition when first obtained, the products 

 being an efflorescence of sulphur in one instance, and in others 

 the formation of sulphate. The latter was also in itself altered 

 by the partial conversion of the FeO into Fe 2 O 3 , its solution 

 yielding an abundant blue precipitate with ferrocyanide of potas- 

 sium ("yellow prussiate"). 



4. Molybdenite, MoS 2 . — Several veins of quartz in which this 

 mineral is abundantly distributed occur on the shore of Sea-beach 



